Yamaha Starbike Forum banner

1 - 20 of 44 Posts

·
Registered
Joined
·
23 Posts
Discussion Starter #1
As the title says, I just had stage 2 cobra jets installed in the carbs at the same time I did the 8k maintenance. Now once the bike gets hot it idles down and turns off.... but will start right back up no problem..... original shop says it needs a valve adjustment and quoted $1k, second opinion shop says fuel delivery and the carbs need gone through again for $390. Hiw can I test this before spending that kind of money?
 

·
Registered
Joined
·
6,638 Posts
Why did you change the jets in the carbs?

Did you recently change the exhaust or intake pods and filters?

Was the bike running correctly when you took it in for maintenance?
 

·
Registered
Joined
·
6,638 Posts
I just looked up your posts from last year. When you got the bike it had straight pipes on it.

Did you get a set of mufflers? How did you determine which jets to put in the carbs?

Normally the jets do not affect the idle - when the bike is idling the main jets are closed.

I doubt that a bike with only 4k miles on it needs its valves adjusted so much that it wont idle. If you have a compression tester, you can tell if the valves are not closing all the way (low compression). But if the bike was running and idling when you took it to get the jets changed, its not the valves.
 

·
Registered
Joined
·
6,638 Posts
By any chance has the bike been parked for the last year with the same fuel in the tank?

That is the #1 problem we see on here, old gas.
 

·
Registered
Joined
·
23 Posts
Discussion Starter #5
I did put mufflers on it and moved down to Florida so I figured it needed the carbs reworked due to adding pipes and all. The shop saying it was valves said riding it in cold weather with shorties could damage the valves and since I rode year round through 45 degree weather at times that could have caused it.

I personally am leaning towards a fuel/air issue. I told them when I wanted the carbs done that I wanted a little more performance out of it if possible and his suggestion was a cobra jet kit. So that is what we went with.

The bike has not been sitting for any extended amount of time until this past month.
 

·
Super Moderator "Loose Nut"
Joined
·
6,642 Posts
Sounds like the carbs were not done properly. I'm with KCW, valves should be good at 4k miles. Normally a "kit" is not needed for carbs to eliminate a lean condition from opening intake or exhaust. All that's needed are two $5 jets and maybe a new gasket. If proper jets were installed you might just need to sync the carbs. Carbs MUST be synced any time you mess with them. By the way, when ever a "mechanic" suggests a carb kit he is trying to up the price, just my opinion. Here is a good read on jetting carbs.

https://sites.google.com/site/vstar1100kb/home/tuning/carb-jetting
 

·
Registered
Joined
·
6,638 Posts
maybe its only the way you worded your post but:

1. to adjust the valves would take about 2 hours. At a normal shop rate of $75 to $100 per hour that is a $150 to $200 job at the most, plus maybe $20 to replace all four O rings on the tappet covers. You can do it yourself with simple tools in maybe 3 hours if you have any experience turning a wrench.

2. If he meant maybe your valves are burned from running with straight pipes on the bike, then ok maybe a valve job might run $1,000. Before you even consider something that drastic go borrow or buy a compression tester from Advance Auto and do a compression check on your bike. If the compression is low, and putting a teaspoon of oil in the sparkplug hole does not bring it up to normal THEN you have a leaky valve. That might just need to be adjusted, or it might be a burnt valve. If you can change a spark plug you can run a compression test.

3. Running a bike with no mufflers should not push it lean enough to burn the valves, or damage the pistons, unless you put over 20,000 miles on the bike and you rev'd the hell out of the engine all the time.

Lesblank knows carbs and jets. Look up the right jets for a bike with slightly modified exhaust only, they should only be a bit larger than the stock jets that came on the bike. I dont know what a stage two kit is, that sounds like a Harley dealer mod package. If you know what size jets they put in the bike compare that to the standard jet tables for a VS 650.

Normally when a carb has new jets installed you also have to adjust the Pilot Main Screws (PMS) and balance the carbs like Les mentioned. The shop that is asking for another thousand dollars did not do a good job on the bike, if they changed the jets and now it wont idle.
 

·
Registered
Joined
·
23 Posts
Discussion Starter #8
So the bike is at 8k now, I know not much of a difference. The jet kit came about because I bought it with no mufflers (without a rejet) and then added mufflers, I asked if they could give me a bit more power out of the jets and the stage 2 cobra jet was what was suggested, I do not know the specs.

I plan on testing the compression this weekend and testing both the sync of the carbs and the timing next week sometime after a friend loans me the tools.

My biggest thing is they immediately threw bad valves at me and until I got a second and third opinion on it I did not want to pretend I was smarter than the dealer and risk my heads.

I was an auto mechanic for a few years across different car brands but for some reason I can not seem to transfer that to bikes... it spooks me to work on a bike.
 

·
Registered
Joined
·
6,638 Posts
Everything you said sounds good, but there is no reason to check the timing. With the electronic ignition the timing is controlled by a position detector on the crankshaft, and the ECU moves the timing around based on throttle position and (I think) engine rpm. There is no way to adjust the timing, its not like setting points, so there is no way someone could have set the timing wrong.

If the throttle position sensor has failed then the timing wont be advancing correctly, the bike would be sluggish as hell and maybe idle crazy fast. If you are not seeing any indication of those things then check the compression and put the vacuum gauges on and see if the carbs are out of balance.

You are on the right track.

Another thing you can do, just like with any gas engine, if the jets they put in are too big the bike will be running very rich. The exhaust will have that distinct 'old car' carbon smell, and your plugs will turn black on less than one tank of gas. Checking the condition of your plugs is a good indication of the jets being too big or too small. The caviot is you have to have clean (new) plugs in there to begin with then see if the jets are fouling them black or maybe burning them white (jets too small - wrong jets for the bike).

You will pull the plugs out for the compression test, so its a freebee

Dont know if anyone has mentioned this: I tell everyone: if you dont have a torque wrench go get one from harbor freight. Even a cheap one is better than none. A 3/8" drive is all you need.

Nearly everything on a motorcycle that you put a wrench on puts a steel bolt into an aluminum part. There is no 'feel' for tightening bolts into aluminum. It feels snug..snug..snug.. then it strips out. This is the single most important thing to know for a motorcycle, even with simple things like spark plugs (12 ft lbs).

Also if you dont have it already the Yamaha Vstar 650 factory service manual is free online in PDF format. All the torque specs are in there.
 

·
Registered
Joined
·
446 Posts
I was paranoid to work on my old bike, but after watching tons of youtube videos I have basically concluded there isn't really anything you can screw up so badly to really hurt yourself. Sure you can get things out of alignment. But really as long as you don't screw up the gear box your likely be ok, just won't have a running bike, or things will wear strangely.

Working on lawnmowers, cars to a point for most of my life. I have done a few motorcycles, but never to make street legal and never with a manual. So it is kindof new to me to dig into them. Much more enjoyable as getting to service parts on a car seems to require to know where all the special holes are, and tools to get to things. Much more straight forward on a bike, even a supersport isn't too horrible, but they are getting closer to annoying.
 

·
Registered
Joined
·
6,638 Posts
Some of the things you have to look out for working on a motorcycle that are different from cars:

1. if you jack a MC up its easy to knock it over, and its very difficult to raise it up with car jacks.

2. There are side covers on motorcycles that give you access to the mechanical parts behind them. Some have different size bolts in each bolt hole, and if you mix them up when you put the cover back on, the long bolt will hit something internal and cause serious damage.

3. Motorcycle oil is different from car oil, because the clutch is in the oil bath. You have to use oil either labeled for 4 cycle motor cycle engines, or use car or diesel oil that has the bottom half of the SAE lollipop blank - that means there are no additives in the oil (for better gas mileage) and it wont make your clutch slip. Usually the only car/truck oil you can find with no additives are the generic brands (walmart for example).

4. Motorcycles with wire spoke wheels always have inner tubes in the tires . If you get a flat tire on a MC with wire spoke wheels, you cannot repair it with a plug. Cast aluminum wheels with large solid spokes are usually tubeless and can be repaired on the side of the road.

5. and for people who have worked on bicycles all your life, a motorcycle tire is like a car tire. It has a bead that is hard seated on the rim. You cannot change a motorcycle tire (anymore) with a couple screw drivers like you can on a bicycle. (Motorcycle tires use to be like big bicycle tires before the 1970s, not anymore).
 

·
Registered
Joined
·
23 Posts
Discussion Starter #12
Thank you guys for the advice, I havent had any time to tear into it unfortunately with working on both of my cars and working 13 hour nights. I will work on it tomorrow when I get some tools from a bike mechanic friend of mine.

My first step is to test the compression, as far as it running rich KCW after the jet kit install my bike now has an afterburn with i pretty concussive pop that you can feel but only at idle so I am pretty sure it is running rich. Is there any possible direction to precede without re jetting it again to standard jets? (I like the slight addition in power and top speed I get) maybe hotter plugs to burn more fuel etc.

<iframe src="https://www.facebook.com/plugins/video.php?href=https%3A%2F%2Fwww.facebook.com%2Ftaylor.freeman.370%2Fvideos%2F2109354719077472%2F&show_text=0&width=846" width="846" height="476" style="border:none;overflow:hidden" scrolling="no" frameborder="0" allowTransparency="true" allowFullScreen="true"></iframe>

after the compression test if it proves the valves are fine (which Im sure they are) I will have to get a few oil guages or something with vacuum lines to check the sync on the carbs and make sure they are properly sync'd. I just have to find the vacuum ports to hook into, havent had a lot of experience with bike carbs.

Overall I just want to make sure that everything is up to par before taking it to a shop and them trying to sell me services that arent needed or if i need to make the shop that did the original work to redo it correctly.

I will keep you guys updated
 

·
Registered
Joined
·
446 Posts
I wouldn't adjust the spark plug temp. It won't burn more gas, it just burns more that sticks to the plug itself to keep the plug clean, doesn't affect anything going out the exhaust.

Where in florida are you at? I'm in ocala and could probably stop over and help out.
 

·
Registered
Joined
·
23 Posts
Discussion Starter #16
I wouldn't adjust the spark plug temp. It won't burn more gas, it just burns more that sticks to the plug itself to keep the plug clean, doesn't affect anything going out the exhaust.

Where in florida are you at? I'm in ocala and could probably stop over and help out.
I am down in Ft. Lauderdale, I am going to mess with it tomorrow once I pick up a few things to test the carbs sync
 

·
Registered
Joined
·
23 Posts
Discussion Starter #18
That would be pretty rough /forums/images/smilies/frown.gif 4.5hour drive approx from here in ocala.
Yeah I used to drive up to Gainsville, thanks for the offer though. With all the help you guys have given I am sure I will be able to pin point the issue or at least provide you with more precise information as to what is happening
 

·
Registered
Joined
·
23 Posts
Discussion Starter #19
Alright guys got an actual carb sync guage. While I have adjusted it it will not sit at 0. This is what I am seeing.

As for when it runs, at temperature no choke,it bounces violently back and forth all while staying in the red, same distance as well
 

Attachments

·
Registered
Joined
·
6,638 Posts
"...While I have adjusted it it will not sit at 0..."

Im not sure what you are trying to do here.

The engine needs to be warmed up, a good 3 to 5 mile ride. Then the idle needs to be set to 1200 rpm.
Then to balance the carbs you want both gauges to read the same number while its idling. Maybe thats what you mean, zero out the difference?

Im not sure what the vacuum reading should actually be at idle connected to those balance ports. If you think the vacuum is low something is leaking somewhere, or there is blowback thru a tight or leaky valve.

If the needles are jumping all over... I would have to look that up to see what that means.
 
1 - 20 of 44 Posts
Top